In an electrophotographic image forming apparatus (e.g., a multi-functional peripheral), an image is obtained by developing a latent image formed on a photoconductor with toner supplied from a development device and transferring the toner image to a medium (e.g., a sheet of paper or a resin sheet). Typically, when the toner is consumed for such developing, new toner is supplied to the development device. Toner in the development device is circulated in the development device to prevent uneven distribution of the toner, during image forming operations.
A concentration of the toner in the development device is detected by a toner concentration sensor provided in the development device. When the detected concentration of the toner in the development device is below a predetermined level, the print operation is suspended and a toner supply operation is carried out to prevent decrease in print quality or other problems such as carrier adhesion. If the toner in the development device is not sufficiently distributed therein, the toner concentration sensor can make an inaccurate detection, which leads to termination of the toner supply operation even though the concentration of the toner in the development device has not returned to a sufficient level for printing.